Although gender coding would suggest that I must have looked upon the idea of seeing the female-oriented romantic comedy “Because I Said So” with the same kind of wariness usually reserved for root canals or screenings of “Epic Movie,” I must confess that this was not quite the case for me. After all, it stars Diane Keaton, who is both a living legend of the genre thanks to “Annie Hall” and the kind of quirky presence who can usually bolster up even substandard material simply with her oddball presence. Keaton’s co-star here is Mandy Moore, the talented singer-actress who has demonstrated a lot of charm and nice comic timing in films both good (“How to Deal” and “Saved”) and bad (“Chasing Liberty” and “American Dreamz”) and if that weren’t enough, one of the key supporting roles is filled by none other than Piper Perabo, about whom I have lucubrated at length in this space many times in the past. Throw in the MPAA’s promise of “partial nudity” and as the lights grew dim, I looked upon the upcoming film with something resembling guarded optimism.

Alas, the guarded optimism I felt was almost instantaneously stripped away and replaced at various times with boredom, confusion, hatred, misery and the desire to slip into the theater next door to catch the last hour of “Babel” in order to cheer myself up. Even by the standards of the kind of poorly conceived romantic comedy trash that usually gets dumped into theaters on Super Bowl weekend in order to score a few bucks from an otherwise underserved audience (such as “The Wedding Date” or “The Wedding Planner”), “Because I Said So” comes up pathetically short. At a certain point, I almost became convinced that it wasn’t a movie at all but a form of Ludovico-style treatment designed to cure me of my affections for Perabo and Moore forever. Well, while I may not have been fully cured, O my brothers, I do suspect that if I think of this film again in the future, it will be accompanied by screaming, vomiting and a desire to hurl myself out of the nearest window.

In the film, Diane Keaton plays Daphne, a woman who is self-absorbed, clingy, controlling and monstrously indifferent to anyone’s feelings but her own–of course, in a film like this, these attributes are seen as virtues instead of flaws. I think we are supposed to be impressed by her tenacious and indomitable spirit because she raised three daughters by herself after her evil husband walked out on her. Of course, after listening to her prattle on for more than three minutes, you will be more impressed over how the unseen husband managed to stick around long enough to father three children with her without succumbing to the urge to chop her into something resembling haggis. Anyway, after her two older daughters–Maggie (Lauren Graham) and Mae (Perabo)–have managed to grow up and get married with only minor emotional scarring, Daphne decides to obsessively throw herself into finding an ideal mate for youngest daughter Milly (Moore), who has just been dumped by the latest in a string of losers and despair of ever finding true love, a fairly unlikely occurrence for anyone even vaguely resembling Mandy Moore. When Milly sensibly thinks that this is going too far over the line–and this is coming from someone who cheerfully called her mother and sisters post-conquest to discuss the aesthetics of her man’s uncircumcised works–Daphne does the only thing that any sane and rational mother in her situation would do. She surreptitiously takes out a personal ad announcing that she is looking for a life partner for her daughter and begins interviewing applicants. I don’t want to suggest that this plot premise is creepy or unpleasant but the last time I can remember a theoretical comedy in which a parent took this much of an unhealthy interest in who their child was dating, it was the Tony Danza epic “She’s Out of Control” and Lord knows we all recall how well that turned out.

After the expected montage of freaks, weirdos, fatties, drag queens and punkers (yes, this is a film that still thinks that the sight of a guy in leather with a nose ring is worth an instant laugh), Daphne comes across Jason (Tom Everett Scott), a handsome young architect who is so seemingly perfect in every conceivable way that he comes across as a potential serial killer. Nevertheless, Daphne thinks that he is a delight and contrives a way in which he can “meet” Milly and sweep her off her feet. At the same time, handsome young musician Johnny (Gabriel Macht) observes what Daphne is doing, disapproves strongly and then surreptitiously lifts one of Milly’s business cards so that he can “meet” her as well. As a result, Milly is now inundated with the attentions of two dreamy guys at the same time and she does what any sweet, sensible girl in her place would do–she cheerfully decides to date both of them at the same time while keeping each one a secret from the other. Of course, Daphne disapproves of Johnny–after all, he is a musician with a tattoo!–and does her best to steer Milly in the direction of Jason, even as she begins to find herself attracted to Johnny’s equally hunky and laid-back father (Stephen Collins).

I am perfectly aware that even the best romantic comedies usually rely on a certain amount of unbelievable character behavior and plot developments in order to get from point A to point B to happy ending (hell, even Shakespeare himself wasn’t immune to it, as anyone who has tried to analyze “Twelfth Night” in depth can attest”) but what transpires in “Because I Said So” goes beyond acceptable implausibility into the realms of outright psychosis. For starters, we are supposed to believe Daphne is the kind of strong, independent woman who single-handedly raised three daughters after a failed marriage–why, then, would she be so obsessed with marrying off her daughter in the first place after her own less-than-successful venture? As for Milly, we are supposed to see her as a sweet-natured girl who is so thunderstruck by simultaneously meeting two perfect guys that she is genuinely torn between the two. Of course, by dating both at the same time (as well as sleeping with them), she comes across as less a confused romantic than as an indecisive slut. She also comes across as an idiot as well because the slick architect character is so cold, oily and creepy–imagine a less cuddly version of Patrick Bateman–that the only plausible reason that she could possibly have for staying with him (especially after the way he freaks out when she accidentally breaks one of his candlesticks) is because she knows that she is in a crappy romantic comedy and she can’t shed him for good until the final reel. (And while we are on the subject, if Hollywood is going to persist in giving us romantic comedies in which a woman is forced to choose between two suitors, can’t they freshen it up a little bit by making the suitors equally likable instead of blatantly tipping the scales in order to make the final choice a little more suspenseful?)

Amazingly, “Because I Said So” was directed by Michael Lehmann, the once-promising director of the cult classic “Heathers” and the criminally underrated “Hudson Hawk.” At this point, I think I am supposed to ask why the man who made such weirdly off-beat comedies as those is doing at the helm of one as profoundly vanilla as this one. Instead, I am more curious as to how he could have made those earlier films at all considering the complete lack of comedic flair or timing that he demonstrates here. For starters, he never finds the right tone for the material for an instant. The allegedly comedic scenes consistently fall flat, the allegedly poignant scenes inspire giggles and his attitude towards his two main characters borders on outright contempt. Perhaps realizing that the central comedic conceit of the film is not even remotely amusing, he and screenwriters Karen Leigh Hopkins & Jessie Nelson (who previously collaborated on the slightly more amusing “Stepmom”) have larded it with the kind of hoary comedy cliches that you thought had been retired years ago–in about 100 minutes, we are treated to such sights and sounds as an adorable dog, wacky foreigners, a little kid who runs around saying “vagina,” people getting smashed in the face with cakes and someone accidentally stumbling onto the kind of adult website that instantly presents all the smut without once asking for a credit card number. All that is missing is a wisecracking pal named Booger, someone wearing a giant pair of sunglasses and that “Oh Yeah” song on the soundtrack–then again, those elements may well turn up in the deleted scenes section of the DVD.

The most scandalous aspect of the film, however, is Lehmann so completely wastes the talented cast that was somehow lured into taking part in the project. The usually likable and endearing Mandy Moore is anything but here–her character is a twit from the get-go and it is impossible to work up any sort of sympathy for her for even a second. Keaton is even more annoying as the latest in her series of overbearing mom roles (including such previous losers as “The Other Sister” and “The Family Stone”) and this could actually be the low point of her entire career–seeing her getting splattered with cake, abused by a masseuse or struggling with the navigation system in her car (which only makes sense if she bought the car maybe five minutes earlier) could well be the single most depressing thing that you’ll see in a film this year. The two guys are as boring as can be and contribute little more to the film other than filling up part of the frame. However, the biggest and most inexplicable casting sin is that the film brings in the likes of Lauren Graham and Piper Perabo–two merry presences with plenty of charm and crack comic timing between them–and then fails to give either of them anything to do. Graham, playing a therapist, get a couple of lame scenes with a neurotic patient (an equally wasted Tony Hale in the least effective cameo from a former star of “Arrested Development” since Jason Bateman popped up in “Smokin’ Aces” last week) while Perabo’s chief contribution is to spend most of one scene wearing a thong. (Then again, I guess I shouldn’t complain since that is the only element of the film that doesn’t hurt too bad when you think about it later.)

“Because I Said So” is a strident, unfunny and wildly unpleasant work that has the artistic finesse and moral center of a low-grade porno film but not the wit and charm. In fact, I almost feel as though I am defaming the good name of romantic comedies by suggesting that it may even tangentially belong to the genre in the first place. Those in the mood for a romantic comedy to watch this weekend are advised to go to their local video store and rent “Bringing Up Baby.” If that is out, try “Say Anything” or “Adam’s Rib” or “Annie Hall.” If those are out, you could pretty much blindly choose any title off the wall–“Dogville,” “Year of the Horse,” “Equus” or Meg Ryan’s entire filmography (including “In the Cut” and that boxing movie)–and be assured that no matter what you may have selected, it will be a better example of the genre than “Because I Said So.”